One common approach to eliminate a base color of a manuscript in an image processing device is to determine a threshold value of luminance and replace pixels of more than the threshold value with white ones. The threshold value used for base elimination can be set to be a value at which the lowest luminance base color is not reproduced. However, when the threshold value is set too low, a high luminance portion of the image in the original manuscript may also be replaced with white. Japanese laid-open patent application H06-46255 discloses an image processing device that is configured to be regulated manually so that a user can freely change a threshold value relative to an average luminance value of a base value detected in an image data.
However, such manual regulation is difficult for the user when there is a color image region on the manuscript similar to a color of the base. The present disclosure includes following configurations so as to alleviate the problem mentioned above.